It sounds like you are on the right path by pursuing your COHN.
Look for employee health nurse jobs in a hospital setting or occupational health nurse jobs at places like Concentra, Takecare Health, or CHS to name a few.
Most industrial occ health jobs look for both the COHN certification and ER experience. Emergency response is important because usually you are the only medical professional on campus. So if someone has an accident or cardiac event, it's just you until EMS gets there. This is where you have an advantage with ER experience.
The non-nursing piece of occupational health is being able to do presentations and write ROI reports. ROI reports are "return on investment" (you have to justify your pay). Show that you can reduce worker's comp costs (through your stellar case management) and reduce of work site injuries (perhaps through your safety education of workers).
I'm suggesting that if this is not your strength, then join a "toastmasters club" to help with the public speaking and take a class on report writing and/or a Microsoft office review.
Hope this helps!